Heretofore, sockets have been proposed that include a base having a cover slidably mounted thereon. The sliding motion between the base and cover is controlled in numerous manners in conventional zero insertion force (ZIF) or low insertion force (LIF) sockets. For example, U.S. Pat. No. 5,256,080 discloses a bail actuated ZIF socket. U.S. Pat. No. 5,730,615 describes a ZIF PGA socket that uses a flat or plate tool that is inserted into receiving slots in the cover and base. The flat tool is moved between two positions in order to open and close the ZIF socket. U.S. Pat. No. 4,498,725 discloses a prior art PGA socket having a base housing and a moveable cover. An L-shaped lever moves the cover across a top surface of the housing. The lever includes a first arm that is rotatably received in a passage in the socket and a second arm that provides a handle for rotating the first arm.
However, existing sockets have experienced limited applicability to certain processor designs. For instance, many circuit designs are conditioned on PGA chips being arranged in a closely packed manner with respect to one another. At least one conventional socket uses an actuation lever located along one side of the socket and moved in the same direction as the direction of relative movement between the cover and base housing. The lever is moved forward along the side of the socket to drive the cover forward and vice versa. However, as components decrease in size and are located closer to one another, space constraints no longer permit the lever to be located along the side of the socket. Thus, it is desirable to minimize the width of sockets holding the PGA chips.
Also, as chip technology evolves, the number of pins on a single chip increases. The socket achieves a separate electrical contact with each pin on a chip and thus the number of electrical contacts to be maintained by a socket is increased. As the pin/contact count increases, the force required to electrically engage the chip and socket similarly increases. Conventional sockets focus significant actuation forces on small areas on the cover and housing. As the actuation forces increase, various socket designs experience more faults as the housing and cover are unable to withstand the increased loads.
Conventional sockets for high pin count PGA chips generally fall into two categories: Low Insertion Force (and extraction force) also known as LIF, and Zero Insertion Force (and extraction force) also known as ZIF. Due to the high forces of LIF sockets, a tool such as an arbor press is needed to insert the package into the socket and another tool is needed to pull the package from the socket. Insertion is relatively simple since typical chips are able to withstand large forces in compression. Extraction is much more difficult since the package can only be held around the perimeter of the pin field. This can lead to damage to the package due to warping and bending of the package during extraction. This difficulty helped lead to the development of ZIF sockets. ZIF sockets typically employ features such as a sliding cover that actuate and de-actuate the socket. The cover of such sockets must be able to withstand the forces of both actuation and de-actuation. In order to support these forces on both tension and compression, ZIF socket covers need to be thicker. This is a problem since higher speed electrical signals require the socket to be shorter, not taller.
Other socket designs are shown in U.S. Pat. Nos. 5,013,256; 5,123,855; 6,217,361; 6,350,142; and 6,347,951, the disclosures of which are incorporated herein by reference. All of these references show LIF or ZIF style sockets for receiving various style packages. One of the difficulties that exists is that when the packages have high volume arrays, on the order of 1000 positions or more, the typical ZIF or LIF style connectors cannot be used. Multiple design issues compound to cause difficulty in this design, including the tolerances of molding of the housing parts which receive the packages, together with the tolerances of the stamping of the contacts and their alignment in the housing. Thus, with 1000 contacts, even with small frictional insertion forces per contact, the overall extraction or actuation/de-actuation force for the package is unacceptable.
A need remains for an improved socket. It is an object of the preferred embodiments of the present invention to meet this and other needs that will become apparent from the following description, drawings and claims.